Estrogen metabolites in equine ovarian follicles: gas chromatographic-mass spectrometric determinations in relation to follicular ultrastructure and progestin content.

Equine follicular fluid was aspirated at various developmental stages (viable, preovulatory and atretic) determined by ultrastructural study. Estrogens and progestins were analyzed by gas chromatography-mass spectrometry associated with stable isotope dilution. Progesterone and 17-hydroxyprogesterone were the principal progestins of the preovulatory and viable follicles. Among the catechol estrogens, 2-hydroxy-estradiol was particularly abundant in the preovulatory follicle and its definitive identification was made by the scan of a full mass spectrum.